Ultrasonic motor and lens apparatus including the same

ABSTRACT

An ultrasonic motor includes a member to be driven including a contact surface; a vibrator including at least one contact part and a piezoelectric element, the vibrator driving the member to be driven by an ultrasonic vibration excited by the piezoelectric element; a retention part for retaining the vibrator; and a pressurization unit including an elastic member so as to apply an impressing force on the at least one contact part against the member to be driven. The retention part includes an abutting part including a line contact part that receives the impressing force from the elastic member and comes into line contact with the pressurization unit; the abutting part has a shape formed of a part of a cylinder; and a center axis of the cylinder is parallel to the at least one contact part and perpendicular to a driving direction of the member to be driven.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ultrasonic motor for driving amember to be driven by generating an ellipsoidal vibration on animpressed vibrator, and to a lens apparatus using the ultrasonic motor.

2. Description of the Related Art

An ultrasonic motor has been conventionally used as a driving source fordriving, for example, a lens mechanism or a camera, taking advantage ofsilent operation, driving capability from low speed to high speed, andhigh torque output. For example, an ultrasonic motor disclosed inJapanese Patent Application Laid-Open No. 2006-158052 includes anannular member to be driven having a rotation axis, and multiplevibrators each including a contact part coming into contact with theannular member to be driven. The vibrator is retained in a state ofbeing impressed against the member to be driven, rendering the contactpart of the vibrator and the member to be driven in a so-calledpressurized contact condition in which the contact part of the vibratoris pressurized against the member to be driven to bring them intocontact with each other. When an ultrasonic vibration is excited on thevibrator under the pressurized contact condition, an ellipsoidal motionis generated on the contact part of the vibrator, so that the member tobe driven is driven to rotate about the rotation axis of the member tobe driven. The pressurized contact condition of the vibrator withrespect to the member to be driven is obtained by biasing the vibratoragainst the member to be driven with use of a plate spring having aconvex part for impressing the vibrator. The contact part of thevibrator comes into pressurized contact with the member to be driven inan appropriate state by impressing and biasing the vicinity of thecenter of the vibrator with a plate spring having the convex part forimpressing the vibrator.

However, in the ultrasonic motor disclosed in Japanese PatentApplication Laid-Open No. 2006-158052, there is a problem that thecontact part of the vibrator and the member to be driven cannot comeinto pressurized contact in an appropriate state due to a manufacturingerror or deformation of the plate spring.

In addition, in the ultrasonic motor disclosed in Japanese PatentApplication Laid-Open No. 2006-158052, the convex part for impressingthe vibrator is formed on the plate spring, and hence the convex partfor impressing the vibrator and the contact part of the vibrator arelikely to be shifted with respect to each other without keeping aconsistent positional relationship therebetween due to an error betweenmembers, an assembling error, a manufacturing error, or deformation ofthe plate spring at the time of pressurization. Therefore, there is aproblem that a direction of impression by the plate spring is deviated,so that a consistent contact condition cannot be maintained between thecontact part of the vibrator and the member to be driven, and in somecases, a contact failure occurs.

Further, the contact parts of the vibrators are arranged in a drivingdirection of the member to be driven, and hence each vibrator is likelyto be inclined in a direction perpendicular to the driving direction andparallel to the contact part of the vibrator rather than in the drivingdirection. The inclination of the vibrator may cause a problem that apartial contact occurs on the contact part, so that the contact part ofthe vibrator and the member to be driven cannot come into pressurizedcontact in an appropriate state.

SUMMARY OF THE INVENTION

The present invention has been made in order to solve theabove-mentioned problem, and it is an object of the present invention toprovide an ultrasonic motor capable of obtaining an appropriatepressurized contact condition between a contact part of a vibrator and amember to be driven.

An ultrasonic motor comprises: a member to be driven including a contactsurface; a vibrator including at least one contact part that is broughtinto contact with the contact surface, and a piezoelectric element thatis fixed on the vibrator, the vibrator being configured to drive themember to be driven by an ultrasonic vibration excited by thepiezoelectric element; a retention part configured to retain thevibrator; and a pressurization unit including an elastic member so as toapply an impressing force on the at least one contact part against themember to be driven, in which: the retention part includes an abuttingpart including a line contact part that receives the impressing forcefrom the elastic member and comes into line contact with thepressurization unit; the abutting part has a shape formed of a part of acylinder; a center axis of the cylinder is parallel to the at least onecontact part and perpendicular to a driving direction of the member tobe driven.

According to the present invention, it is possible to provide theultrasonic motor that drives the member to be driven by an ultrasonicvibration generated on the vibrator and is capable of obtaining anappropriate pressurized contact condition between the contact part ofthe vibrator and the member to be driven.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of an ultrasonic motor accordingto a first embodiment of the present invention.

FIG. 2 is a perspective view for illustrating an assembled state ofmembers illustrated in FIG. 1.

FIG. 3 is an enlarged perspective view for illustrating a joined stateof a vibrator and a smaller base.

FIG. 4A is an enlarged cross-sectional view for illustrating theassembled state of the members according to the first embodiment.

FIG. 4B is an enlarged cross-sectional view for illustrating theassembled state of the members according to the first embodiment.

FIG. 4C is an enlarged detail view of a portion A illustrated in FIG.4B, for illustrating component vectors of an impressing force of anelastic member.

FIG. 5A is an explanatory view for illustrating an abutting part of thesmaller base, which is formed of a part of a cylinder.

FIG. 5B is a view for illustrating a case where a rotor and a ring baseare inclined in a relative manner.

FIG. 5C is a schematic view for illustrating a positional relationshipbetween a center axis of the cylinder forming the abutting part and aline contact part between the abutting part and a pressurization member.

FIG. 6A is a view for illustrating a case where the center axis of thecylinder is shifted compared to FIGS. 5A to 5C.

FIG. 6B is a view for illustrating a case where the center axis of thecylinder is shifted compared to FIGS. 5A to 5C.

FIG. 7 is an exploded perspective view of an ultrasonic motor accordingto a second embodiment of the present invention.

FIG. 8 is an enlarged cross-sectional view for illustrating an assembledstate of members illustrated in FIG. 7.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

Exemplary embodiments of the present invention are described below withreference to the accompanying drawings. Although a rotary driving typemotor that is formed in a unit as a driving actuator of a lens barrel orthe like for a digital camera is described as an example of anultrasonic motor according to this embodiment, its usage is not limitedto this.

FIG. 1 is an exploded perspective view of an ultrasonic motor accordingto an embodiment of the present invention. In the figures, the samemembers are represented by the same reference symbols. As illustrated inFIG. 1, the ultrasonic motor according to this embodiment includes arotor 101, a vibration plate 102, a piezoelectric element 103, a smallerbase 104, a ring base 105, a pressurization member 106, and a platespring 107 described later. The rotor 101 is a member to be driven,including a contact surface 101 a with which a vibrator 109 describedlater comes into pressurized contact. The vibration plate 102 is a partin contact with the contact surface 101 a under a pressurized contactcondition involving an impression. The piezoelectric element 103 istightly adhered to the vibration plate 102 with an adhesive or the like.When a voltage is applied to the piezoelectric element 103 in a state inwhich the piezoelectric element 103 is tightly adhered to the vibrationplate 102, an ultrasonic vibration is generated, so that an ellipsoidalmotion can be generated on the vibration plate 102. The vibration plate102 and the piezoelectric element 103 constitute the vibrator 109. Inthis embodiment, the vibrator 109 is provided at three points, thusdriving the rotor 101 to rotate. The smaller base 104 is a retentionmember for retaining the vibrator 109. The ring base 105 is a fixingmember for retaining the smaller base 104, and the pressurization member106 and plate spring 107. The pressurization member 106 is fitted into athrough hole part 105 b of the ring base 105, and is retained to moveonly in a direction substantially perpendicular to the contact surface101 a of the rotor 101, thus causing the vibrator 109 to come intopressurized contact with the rotor 101 via the smaller base 104 by animpressing force from the plate spring 107. The plate spring 107 servesas an elastic member, which is fixed to the ring base 105 with a screw108 at each end portion thereof, and causes the vibrator to come intopressurized contact with the member to be driven by an impressing forceof the plate spring. The pressurization member 106 and the plate spring107 constitute a pressurization unit of the present invention.

As described above, the above-mentioned members are assembled in a unitas an ultrasonic motor.

FIG. 2 is a perspective view for illustrating an assembled state of themembers illustrated in FIG. 1. In FIG. 2, a configuration around thevibrator 109 is the same for all three points, and hence, to simplifythe figure, the reference symbols are assigned only to a front side inthe figure. As illustrated in FIG. 2, at each of the three points of thering base 105, an impressing force is applied to the vibrator 109 by theplate spring 107 that is fixed with the two screws 108 via thepressurization member 106 and the smaller base 104, and as a result, thevibrator 109 and the contact surface 101 a of the rotor 101 come intopressurized contact with each other. When actually mounting theultrasonic motor on the lens barrel or the like, the rotor 101 iscoupled to a focusing mechanism or a zoom mechanism for driving.

Hereinafter details on the structural members of the ultrasonic motorare described. FIG. 3 is an enlarged perspective view for illustrating ajunction state of the vibration plate 102 and the smaller base 104illustrated in FIGS. 1 and 2 as viewed from the rotor 101 side. Asillustrated in FIG. 3, two protruded parts are formed on a plate part102 a at the center of the vibration plate 102. A protruded contactsurface 102 b is formed on an upper end surface of the protruded partand functions as a contact part that comes into contact with the contactsurface 101 a of the rotor 101. Two protruded contact surfaces 102 b areformed on the same plane, and finished as uniform surfaces by polishingor the like at the time of manufacturing in order to ensure anappropriate contact condition with the contact surface 101 a of therotor 101.

On the other hand, the piezoelectric element 103 is tightly adhered to aback surface side of the plate part illustrated in FIG. 3 (a surfaceside opposite to the surface on which the two protruded parts areformed) with an adhesive or the like. The method of tightly adhering thepiezoelectric element 103 to the back surface of the plate part 102 a isnot limited as long as the two components are tightly adhered to eachother. The piezoelectric element 103 includes multiple piezoelectricelement films laminated and integrated. An application of a desiredalternate-current (AC) voltage to the piezoelectric element 103 formedby laminating the multiple piezoelectric element films causes avibration, thus exciting two vibration modes on the vibration plate 102having the piezoelectric element 103 tightly adhered thereto. At thistime, by setting vibration phases of the two vibration modes to obtain adesired phase difference, an ellipsoidal motion is generated on theprotruded contact surfaces 102 b as indicated by arrows illustrated inFIG. 3. The ellipsoidal motion is generated on the vibrators 109 at thethree points as illustrated in FIGS. 1 and 2 and transferred to thecontact surface 101 a of the rotor 101, so that the rotor 101 can bedriven to rotate. Details on the above-mentioned laminated structure ofthe piezoelectric element and the above-mentioned vibration mode aresubstantially the same as the contents described in Japanese PatentApplication Laid-Open No. 2004-304887. The entire content of JapanesePatent Application Laid-Open No. 2004-304887 is hereby incorporated byreference as if presented herein in its entirety.

Two junction parts 102 c for joining to higher upper surface parts 104 aformed on both sides of the smaller base 104 are formed on both ends ofthe vibration plate 102. Although the vibration plate 102 is joined tothe smaller base 104 by welding or adhering at the junction part 102 c,the method of joining the vibration plate 102 and the smaller base 104is not limited as long as the vibration plate 102 and the smaller base104 are joined to each other. Two arm parts 102 d are formedrespectively between the two junction parts 102 c and the plate part 102a, and the plate part 102 a to which the piezoelectric element 103 istightly adhered is fixed to the smaller base 104 via the arm parts 102d. The arm parts 102 d are formed into a narrower shape than the platepart 102 a and the junction part 102 c as illustrated in FIG. 3 toachieve such a configuration that hardly transfers the vibrationgenerated on the plate part 102 a to the junction part 102 c. In otherwords, a coupling configuration for preventing the vibration generatedon the plate part 102 a from being interrupted by the smaller base 104that is a rigid member is achieved by the arm parts 102 d. In addition,a predetermined space 203 is formed between a flat part 104 b near thecenter of the smaller base 104 and a surface (not shown) of thepiezoelectric element 103 facing the flat part 104 b.

FIGS. 4A and 4B are enlarged cross-sectional views for illustrating theassembled state of the members, in which the rotor 101 is located on theupper side and only a surrounding area of one of the three vibrators 109illustrated in FIG. 2 is illustrated in an enlarged manner. The othertwo vibrators have the same configuration, and a description thereof isomitted.

FIG. 4A illustrates a cutting plane on a plane that is parallel to thedriving direction of the rotor 101 and includes a center of gravity of awhole protruded contact surface including the two protruded contactsurfaces 102 b coming into contact with the contact surface 101 a of therotor 101 and a normal line of the contact surface 101 a of the rotor101 originating at the center of gravity.

FIG. 4B illustrates a cutting plane on a plane including a center ofgravity of the whole protruded contact surface coming into contact withthe contact surface 101 a in the vibration plate 102 illustrated in FIG.3 and a normal line of the contact surface 101 a, and perpendicular tothe view illustrated in FIG. 4A.

However, the whole protruded contact surface is a surface including allthe protruded contact surfaces 102 b, and includes the two protrudedcontact surfaces 102 b in the example illustrated in FIG. 4A. Inaddition, the center of gravity of the whole protruded contact surface(hereinafter, also referred to as a “whole contact gravity center part”)also includes an intersection point of a center line 201 described laterwith the contact surface 101 a.

In FIGS. 4A and 4B, the center line 201 is a line passing through thecenter of gravity of the whole protruded contact surface coming intocontact with the contact surface 101 a in the vibration plate 102 andincluding the normal line of the contact surface 101 a.

The protruded contact surfaces 102 b come into contact with the contactsurface 101 a of the rotor 101, and are held in a pressurized contactcondition. In addition, the junction parts 102 c on both ends of thevibration plate 102 are joined to the smaller base 104 at the two uppersurface parts 104 a. The predetermined space 203 is then formed betweenthe piezoelectric element 103 and the flat part 104 b of the smallerbase 104.

A hole part 104 c and an elongated hole part 104 d are provided on thelower surface side of the smaller base 104, and two shaft parts 105 aformed on the ring base 105 are respectively fitted therein. An abuttingpart 104 e is provided on the lower center of the smaller base 104. Theabutting part 104 e has an arc shape in cross section illustrated inFIG. 4A, which is a part of a cylinder extending in a direction of thedepth of the drawing sheet (a lateral direction in FIG. 4B). An upperend surface 106 a of the pressurization member 106 comes into contactwith the abutting part 104 e at a line contact part 106 c. The upper endsurface 106 a is formed as a flat surface, and hence the contact withthe abutting part 104 e at the line contact part 106 c is a line contacthaving a length in the direction of the depth of the drawing sheet inFIG. 4A (the lateral direction in FIG. 4B). Although the abutting part104 e is a part of a shape formed of a cylinder having an arc shape asdescribed above in this embodiment, the shape of the abutting part 104 eis described later in detail with reference to FIGS. 5A, 5B, and 5C.

The ring base 105 includes the through hole part 105 b on a surfacefacing the plate spring 107 as illustrated in FIG. 1, and thepressurization member 106 comes into contact with the plate spring 107by being fitted in the through hole part 105 b, thus cooperating withthe plate spring 107. The center axes of the through hole part 105 b andthe pressurization member 106 substantially match the center line 201,i.e., an axial direction perpendicular to the contact surface 101 a. Theplate spring 107 is deformed to come into contact with a sphericalsurface part 106 b on the lower side of the pressurization member 106 inFIGS. 4A and 4B in a state in which the pressurization member 106 isbiased against the smaller base 104 by an elastic force.

The plate spring 107 needs to have a reduced spring constant to someextent in order to reduce a fluctuation of the impressing force due to achange of a deformation amount. Therefore, it is desired that the platespring 107 be as thin as possible and the plate spring 107 be as long aspossible. The plate spring 107 according to this embodiment is formedwith use of a thin plate into an arc shape in order to achieve as largea spring length as possible in the annular ultrasonic motor. With thisstructure, the fluctuation of the impressing force can be suppressedeven when a displace amount of the pressurization member 106 in theimpressing direction is changed to some extent. With the above-mentionedconfiguration, the vibrator 109 is impressed against the rotor 101 bythe plate spring 107 via the smaller base 104 and the pressurizationmember 106.

A configuration for transferring the impressing force by the platespring 107 is described below with reference to FIGS. 4A, 4B, and 4C. Inthe following description, an impressing force vector is a force vectorincluding a direction and a magnitude of the impressing force in thecross section of each figure.

As illustrated in FIG. 4A, the abutting part 104 e of the smaller base104 is held in contact with the pressurization member 106 at the linecontact part 106 c. The smaller base 104 is further held in contact withthe rotor 101 at the protruded contact surfaces 102 of the two protrudedparts, and the center of gravity of each protruded contact surface islocated at the same distance from the center line 201 in the drivingdirection of the rotor. On the other hand, regarding the contact betweenthe plate spring 107 and the pressurization member 106, the plate spring107 is formed into an arc shape in this embodiment, and hence, thesupport parts on both ends of the plate spring 107 and an input point ofthe impressing force (a contact point between the plate spring 107 andthe pressurization member 106) do not exist on a straight line.Therefore, a cross section of the plate spring 107 when generating theimpressing force is in a state having an inclination as illustrated inFIG. 4B. In that case, as a result, the impressing force vector input tothe pressurization member 106 by the plate spring 107 can be indicatedby an arrow (vector) 206 a. The contact point between the pressurizationmember 106 and the plate spring 107 does not exist on the center line201, and in FIG. 4B, the contact point is shifted to a point 205 on theright side of the center line 201.

FIG. 4C is an enlarged detail view of a vicinity of the point 205 in aportion A illustrated in FIG. 4B. The impressing force applied to thepressurization member 106 by the plate spring 107 is represented by thevector 206 a, which is inclined with respect to the center line 201.Therefore, the impressing force vector 206 a includes a component vector206 b in a direction parallel to the center line 201 and a componentvector 206 c in a direction perpendicular to the center line 201.

The pressurization member 106 is retained by the ring base 105 with adegree of freedom only in a direction substantially parallel to thecenter line 201 as illustrated in FIGS. 4A and 4B. That is, thepressurization member 106 is configured to move in a directionsubstantially perpendicular to the contact surface 101 a of the rotor101, and on the other hand, the pressurization member 106 is restrictedto move in a direction substantially parallel to the contact surface 101a of the rotor 101. Therefore, in the impressing force (vector 206 a) ofthe plate spring 107 for impressing the pressurization member 106, aforce (vector 204 a) corresponding to a component (vector 206 b) in thedirection of the center line 201 is transferred to the smaller base 104.

On the other hand, the impressing force (vector 204 a) transferred tothe smaller base 104 is transferred to the protruded contact surfaces102 b of the two protruded parts as an impressing force for the contactsurface 101 a of the rotor, and a force of impressing the contactsurface 101 a by each of the protruded contact surfaces 102 b is a half(vector 204 b) of the impressing force vector 204 a.

The contact between the protruded contact surfaces 102 b and the contactsurface 101 a is a surface contact, and hence, in practice, theimpressing force is evenly distributed on the plane. However, for thesake of better understanding, the impressing force is represented as aforce vector acting on a position of the center of gravity of the plane.Likewise, the contact between the pressurization member 106 and theabutting part 104 e at the line contact part 106 c is a line contact,and hence, in practice, the impressing force is evenly distributed onthe straight line of line contact. However, the impressing force is alsorepresented as a force vector acting on a position of the center ofgravity of the straight line. Hereinafter, the impressing force isrepresented as a force vector at the position of the center of gravityfor both the surface contact and the line contact.

In addition, on a side surface part of the pressurization member 106, africtional force is generated by the component vector 206 c of theimpressing force vector 206 a input to the pressurization member 106 bythe plate spring 107, the component vector 206 c acting in the directionperpendicular to the center line 201. On the other hand, a frictionalforce is also generated on the fitting parts of the shaft parts 105 a.These frictional forces are ignored because these are sufficiently smallwith respect to the impressing force. In practice, if the finishing ofthe side surface is smoothened to some extent, an influence of thefrictional forces can be reduced to a level that can be ignored.

In this embodiment, as described above, the pressurization member 106 issubstantially retained on the ring base 105 in a state of having adegree of freedom only in the direction of the center line 201.Therefore, the impressing force vector 204 a applied to the smaller base104 by the pressurization member 106 can be substantially matched withthe center line 201. At this time, the magnitude of the impressing forcevector 204 a is substantially equal to the component vector 206 b of theimpressing force vector 206 a by the plate spring 107 in the directionparallel to the center line 201. This is because a force correspondingto the component vector 206 b of the impressing force vector 206 a worksas the impressing force vector 204 a. The component vector 206 c of theimpressing force vector 206 a in the direction perpendicular to thecenter line 201 affects the frictional force on the side surface part ofthe pressurization member 106. Through the smooth finishing of thesurfaces, the frictional force generated between the side surface of thepressurization member 106 and an internal surface of the through holepart 105 b is sufficiently small compared to the impressing force, anddoes not interfere with a smooth reciprocating movement of thepressurization member 106. In this manner, as illustrated in FIGS. 4Aand 4B, the point of load of the input impressing force vector 206 a isshifted from the center line 201, and the direction of the impressingforce vector 206 a is not parallel to the center line 201, but the twoprotruded contact surfaces 102 b can maintain an appropriate pressurizedcontact condition with respect to the contact surface 101 a of the rotor101.

By the way, the smaller base 104 is impressed via the line contact parton a straight line of the abutting part 104 e. Therefore, as describedlater, in the cross section illustrated in FIG. 4A, the smaller base 104is configured to be inclined, so that an appropriate pressurized contactcondition can be maintained even when inclination of a member occurs dueto a dimension error at the time of manufacturing, an assembling error,or a disturbance.

A shape of the abutting part 104 e of the smaller base 104 to which animpressing force is applied from the pressurization member 106 isdescribed with reference to FIGS. 5A, 5B, and 5C. FIGS. 5A, 5B, and 5Cillustrate a portion of the same cross section as that illustrated inFIG. 4A.

The abutting part 104 e of the smaller base 104 is formed as an arc sidesurface part formed of a part of a cylinder 205 a extending with an axisof symmetry (center axis) in a direction perpendicular to the crosssection illustrated in FIG. 5A. In FIG. 5A, a center axis 205 b of thecylinder 205 a passes through a point at which the contact surface 101 aof the rotor 101 and the center line 201 intersect with each other,i.e., the center of gravity of the whole protruded contact surface. Theabutting part 104 e comes into contact with the pressurization member106 at the line contact part 106 c. In FIG. 5A, the line contact part106 c intersects with the center line 201. With the above-mentionedconfiguration, a uniform impressing force can be applied between the twoprotruded contact surfaces 102 b and the contact surface 101 a of therotor 101, and as a result, an appropriate pressurized contact conditioncan be maintained.

FIG. 5B illustrates a case where relative inclination occurs between therotor 101 and the ring base 105 compared to the state illustrated inFIG. 5A. FIG. 5C is an enlarged view in which an inclination angle isrepresented in an exaggerated manner for illustrating a positionalrelationship between the center axis 205 b of the cylinder 205 a and theline contact part 106 c when the inclination occurred. In the caseillustrated in FIG. 5B, the line contact part 106 c at which the contactsurface 106 a of the pressurization member 106 comes into contact withthe abutting part 104 e of the smaller base 104 is, as illustrated inFIG. 5C, shifted from the position intersecting with the center line 201in the case illustrated in FIG. 5A. However, the impressing forceapplied to the whole protruded contact surface via the abutting part 104e is constantly directed to the direction of the center of gravity ofthe whole protruded contact surface. Therefore, even in the case whererelative inclination occurs between the rotor 101 and the ring base 105,a uniform impressing force can be applied between the two protrudedcontact surfaces 102 b and the contact surface 101 a of the rotor 101without generating a moment between the two protruded contact surfaces102 b, and therefore, an appropriate pressurized contact condition canbe maintained. Although the ring base 105 is fitted into the smallerbase 104 via the hole part 104 c, the elongated hole part 104 d, and theshaft part 105 a, the inclination can occur because a fitting clearance,i.e., a fitting space is provided.

An amount of the fitting space necessary for the inclination can be setin advance based on the maximum necessary inclination angle for theinclination of the member due to an error between members, a dimensionerror at the time of manufacturing, an assembling error, or adisturbance. The center axis 205 b of the cylinder 205 a indicated by adotted line that forms the abutting part 104 e is set to match a centerpoint between the centers of gravity of the two protruded contactsurfaces 102 b, i.e., the center of gravity of the whole protrudedcontact surface described above. With this configuration, the normalline of the contact surface 106 a of the pressurization member 106 onthe line contact part 106 c is constantly directed to the direction ofthe center axis 205 b of the cylinder 205 a. As a result, the directionof the normal line of the contact surface 106 a (the direction of theimpressing force) at the contact position of the pressurization member106 and the smaller base 104 can be constantly directed to the centerpoint between the two protruded contact surfaces 102 b on the contactsurface 101 a of the rotor 101, and therefore, the impressing forcesbetween the two protruded contact surfaces 102 b and the contact surface101 a of the rotor 101 can be maintained uniform.

Therefore, even when inclination occurs due to an error between membersof the rotor 101 and the ring base 105, a dimension error at the time ofmanufacturing, or an assembling error, or when inclination occurs on amember due to a vibration at the time of driving or a disturbance, theimpressing force applied from the pressurization member 106 via theabutting part 104 e to the two protruded contact surfaces 102 b and thecontact surface 101 a of the rotor 101 is constantly directed to thecenter axis 205 b of the cylinder 205 a with respect to the inclination,and hence a stable pressurized contact condition can be maintainedbetween the two protruded contact surfaces 102 b and the contact surface101 a of the rotor 101.

In the cross section illustrated in FIG. 4B, the smaller base 104 andthe pressurization member 106 are not inclined with respect to eachother in a lateral direction of FIG. 4B through the contact of theabutting part 104 e of the smaller base 104 and the pressurizationmember 106 that is set as a line contact of a straight line.

In addition, in the two protruded contact surfaces 102 b on the crosssection of FIG. 4A, the width of the protruded contact surface 102 b onthe cross section illustrated in FIG. 4B is sufficiently smallercompared to the width between edge parts of the protruded contactsurface 102 b in the driving direction of the rotor 101, and hence thevibrator 102 is likely to be inclined unintentionally in the lateraldirection of FIG. 4B at the time of rotary driving, possibly leading todegradation of the pressurized contact condition. Therefore, in thisembodiment, the length of the line contact part 106 c at which thepressurization member 106 comes into contact with the abutting part 104e of the smaller base 104 on the cross section illustrated in FIG. 4B isset to be longer than the width of the protruded contact surface 102 bon the cross section illustrated in FIG. 4B to support the vibrator 102,with the result that the inclination hardly occurs.

FIGS. 6A and 6B illustrate a case where the center axis 205 b of thecylinder 205 a does not pass through the center point between thecenters of gravity of the two protruded contact surfaces 102 b, i.e.,the center of gravity of the whole protruded contact surface, but passesnearby. FIGS. 6A and 6B illustrate a portion of the same cross sectionas that illustrated in FIGS. 5A, 5B, and 5C.

In FIGS. 5A, 5B, and 5C, the center axis 205 b of the cylinder 205 apasses through the center of gravity of the whole protruded contactsurface. However, there is a case where the center axis 205 b of thecylinder 205 a is hard to pass through the center of gravity of thewhole protruded contact surface due to various constraint conditions inmanufacturing and assembling. In such a case, as illustrated in FIG. 6A,the center axis 205 b is caused to pass through a dividing point 205 cof a line connecting the edge parts of the two protruded contactsurfaces 102 b near the center point in the driving direction of therotor 101. Accordingly, it is possible to maintain a state of biasingthe two protruded contact surfaces 102 b and the contact surface 101 aof the rotor 101 by distributing the impressing force from thepressurization member 106 at a constant ratio. In the configurationillustrated in FIG. 6A, even when relative inclination occurs betweenthe rotor 101 and the ring base 105 as illustrated in FIGS. 5B and 5C,the impressing force from the pressurization member 106 is constantlydirected to the center axis 205 b of the cylinder 205 a. Therefore, itis possible to maintain the state in which the impressing force from thepressurization member 106 is applied by being distributed at theconstant ratio between the two protruded contact surfaces 102 b.

FIG. 6B illustrates a case where the center axis 205 b of the cylinder205 a is shifted in any one of upper, lower, left, and right directionsof the drawing sheet from the center point between the centers ofgravity of the above-mentioned two protruded contact surfaces 102 b,i.e., the center of gravity of the whole protruded contact surface dueto various constraint conditions in manufacturing and assembling. Inthis case, a straight line including the line contact part 106 c and thecenter axis 205 b of the cylinder 205 a on the cross section illustratedin FIG. 6B is configured to intersect the contact surface 101 a of therotor 101 at a dividing point 205 d of a line connecting the edge partsof the two protruded contact surfaces 102 b in the driving direction ofthe rotor 101. With this configuration, the impressing force from thepressurization member 106 is constantly applied between the twoprotruded contact surfaces 102 b, and hence the pressurized contactcondition can be maintained without causing a contact error between thetwo protruded contact surfaces 102 b and the contact surface 101 a ofthe rotor 101. In addition, also in the configuration illustrated inFIG. 6B, when relative inclination occurs between the rotor 101 and thering base 105 as illustrated in FIGS. 5B and 5C, the above-mentionedstraight line is configured to intersect the contact surface 101 a ofthe rotor 101 at the dividing point 205 d of the line connecting theedge parts of the two protruded contact surfaces 102 b in the drivingdirection of the rotor 101. Therefore, the impressing force from thepressurization member 106 is constantly applied between the twoprotruded contact surfaces 102 b, and as a result, the pressurizedcontact condition can be maintained without causing a contact errorbetween the two protruded contact surfaces 102 b and the contact surface101 a of the rotor 101.

As described above, in this embodiment, the abutting part 104 e of thesmaller base 104 that retains the vibrator 109, which is a planereceiving the impressing force, is formed into a shape formed of a partof the cylinder 205 a about the center axis 205 b that passes near thecenter point between the two protruded contact surfaces 102 b, and hencean ultrasonic motor can be realized which can maintain an appropriatepressurized contact condition between the protruded contact surfaces 102b of the vibrator 109 and the contact surface 101 a of the rotor 101.

Although the configuration in which the two protruded contact surfaces102 b achieve the pressurized contact condition between the twoprotruded contact surfaces 102 b and the contact surface 101 a of therotor 101 is described in this embodiment, the present invention is notlimited to this configuration.

A single protruded contact surface 102 b may be provided. When a singleprotruded contact surface is provided, the whole protruded contactsurface is the same as the single contact surface. A center of gravityof the single contact surface is matched substantially on the centerline 201. With this configuration, an appropriate pressurized contactcondition can be maintained. In addition, three or more protrudedcontact surfaces may be provided. When three or more protruded contactsurfaces are provided, in the same manner as the case where the twoprotruded contact surfaces are provided, a center of gravity of thewhole protruded contact surface including the three or more protrudedcontact surfaces is matched substantially on the center line 201. Withthis configuration, an appropriate pressurized contact condition can bemaintained.

In addition, even when multiple protruded contact surfaces are providedand shapes of the protruded contact surfaces are different from oneanother, a center of gravity of the whole protruded contact surfaceincluding the multiple protruded contact surfaces is matchedsubstantially on the center line 201. With this configuration, anappropriate pressurized contact condition can be maintained, and theeffect of the present invention can be achieved.

Second Embodiment

A second embodiment of the present invention is a modification exampleof the first embodiment, in which the three plate springs 107corresponding to the three pressurization members 106 are integrallyformed. With this configuration, the number of plate springs 107 andscrews 108 can be reduced, achieving an effect of cost reduction.

FIG. 7 is an exploded perspective view of an ultrasonic motor accordingto the second embodiment of the present invention. In the figure, thesame members are represented by the same reference numerals, and thesame members as those of the first embodiment are also represented bythe same reference numerals. In the second embodiment, a ring base 301only includes shaft parts 105 a for positioning the smaller base 104 andthrough hole parts 105 b for respectively fitting the pressurizationmembers 106 therein. A washer 302 is retained in contact with the threepressurization members 106. A wave washer 303 is provided to impress thewasher 302. A fixing unit (not shown) is provided on the upper side ofthe wave washer 303, and by sandwiching the wave washer 303 between thefixing unit and the washer 302, a wave form of the wave washer 303 isdepressed by a predetermined amount to generate an impressing force.

FIG. 8 is an enlarged cross-sectional view for illustrating an assembledstate of members according to the second embodiment. In FIG. 8, the wavewasher 303 is depressed by the predetermined amount, and the impressingforce is transferred to the pressurization member 106 via the washer302. A configuration of transferring the impressing force in thesubsequent stage is the same as that of the first embodiment.

By the way, in the first embodiment, the plate spring 107 is fixed onthe ring base 105, and hence an absolute position of the ring base 105in the direction of the center line 201 in FIGS. 4A and 4B is determineddepending on a deformation amount of the plate spring 107. However, inthe second embodiment, the ring base 301 only takes a role of retainingthe smaller base 104 and the pressurization member 106, and the wavewasher 303 is not fixed. Thus, the position of the ring base 301 in thedirection of the center line 201 is not determined. Therefore, whenmounting the ultrasonic motor according to the second embodiment to alens barrel or the like, the ring base 301 may be fixed to have adesired absolute position with respect to a fixed cylinder in thebarrel, so that the ring base 301 does not move unintentionally.Alternatively, the ring base 301 may be integrated with the fixed barreldepending on the configuration.

Therefore, in the second embodiment, the single wave washer 303 iscommonly used as the elastic member for impressing the threepressurization members 106, and hence there is no need for the platespring and the screw, achieving the cost reduction.

Third Embodiment

According to a third embodiment of the present invention, a lensapparatus having the effect of the present invention can be achieved byemploying the ultrasonic motor according to the first or secondembodiment as a driving unit for driving a focusing lens or a zoom lensin the lens apparatus.

As described above, in the ultrasonic motor that drives the member to bedriven by an ultrasonic vibration generated on the vibrator, anappropriate pressurized contact condition can be achieved between theabutting part of the vibrator and the part to be contacted by causingthe center axis of the shape formed of a part of a cylinder forming thecontact part of the smaller base to pass near the whole contact gravitycenter part.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2011-204002, filed Sep. 20, 2011, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A driving apparatus, comprising: a memberincluding a contact surface; a vibrator including at least one contactpart that is brought into contact with the contact surface, and apiezoelectric element, wherein the vibrator is configured to move themember relatively to the vibrator by a vibration excited by thepiezoelectric element; a pressing unit comprising an elastic member soas to apply an impressing force on the at least one contact part againstthe member; and a contact member configured to contact the pressing unitand being located between the pressing unit and the vibrator, whereinthe contact member comprises an abutting part including a line contactpart that receives the impressing force from the elastic member andcomes into line contact with the pressing unit, the abutting part has ashape formed of a part of a cylinder, and a center axis of the cylinderis parallel to the at least one contact part and perpendicular to adriving direction of the member.
 2. The driving apparatus according toclaim 1, wherein in a cross-section parallel to the driving direction ofthe member to be driven and including a normal line of the contactsurface at a whole contact gravity center part of the at least onecontact part, a straight line passing through the line contact part andthe center axis passes through a dividing point of a line including endparts of the at least one contact part in the driving direction.
 3. Thedriving apparatus according to claim 2, wherein the center axis passesthrough the dividing point of the line including the end parts of the atleast one contact part in the driving direction.
 4. The drivingapparatus according to claim 3, wherein the center axis passes throughthe whole contact gravity center part.
 5. The driving apparatusaccording to claim 1, wherein in a direction of the center axis of thecylinder, a length of the line contact part is larger than a width ofthe at least one contact part in a direction perpendicular to thedriving direction.
 6. The driving apparatus according to claim 1,wherein the pressing unit further comprises: a pressing member thattransfers the impressing force from the elastic member to the abuttingpart; and a fixing member that allows the pressing member to move in adirection perpendicular to the contact surface and restricts thepressing member from moving in a direction parallel to the contactsurface.
 7. The driving apparatus according to claim 1, wherein theelastic member is a plate spring.
 8. The driving apparatus according toclaim 1, wherein the elastic member is a wave washer.
 9. A lensapparatus, comprising the driving apparatus according to claim 1.